Cooperative caching for efficient data access in disruption tolerant networks

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COOPERATIVE CACHING FOR EFFICIENT DATA ACCESS IN
DISRUPTION TOLERANT NETWORKS
ABSTRACT
Disruption tolerant networks (DTNs) are characterized by low node density,
unpredictable node mobility, and lack of global network information. Most of
current research efforts in DTNs focus on data forwarding, but only limited work
has been done on providing efficient data access to mobile users. A novel approach
is proposed to support cooperative caching in DTNs, which enables the sharing and
coordination of cached data among multiple nodes and reduces data access delay.
The basic idea is to intentionally cache data at a set of network central locations
(NCLs), which can be easily accessed by other nodes in the network. To propose
an efficient scheme that ensures appropriate NCL selection based on a probabilistic
selection metric and coordinates multiple caching nodes to optimize the tradeoff
between data accessibility and caching overhead. Extensive trace-driven
simulations show that this approach significantly improves data access
performance compared to existing schemes.

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OBJECTIVE OF STUDY
Objective is to efficiently support cooperative caching in DTNs. For this, to
propose a method to cache data at a set of network central locations (NCLs), each
of which corresponds to a group of mobile nodes being easily accessed by other
nodes in the network. To ensure that popular data are always cached nearer to the
central nodes via dynamic cache replacement based on query history. To propose a
data access scheme to probabilistically coordinate multiple caching nodes for
responding to user queries.
INTRODUCTION
Disruption tolerant networks (DTNs) consist of mobile devices that contact each
other opportunistically. Due to the low node density and unpredictable node
mobility, only intermittent network connectivity exists in DTNs, and the
subsequent difficulty of maintaining end-to end communication links makes it
necessary to use “carry and- forward” methods for data transmission. Examples of
such networks include groups of individuals moving in disaster recovery areas,
military battlefields, or urban sensing applications. In such networks, node
mobility is exploited to let mobile nodes carry data as relays and forward data
opportunistically when contacting others. The key problem is, therefore, how to
determine the appropriate relay selection strategy.
Although forwarding schemes have been proposed in DTNs, there is limited
research on providing efficient data access to mobile users, despite the importance

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of data accessibility in many mobile applications. For example, it is desirable that
smart phone users can find interesting digital content from their nearby peers. In
vehicular ad-hoc networks (VANETs), the availability of live traffic information
will be beneficial for vehicles to avoid traffic delays. In these applications, data are
only requested by mobile users whenever needed, and requesters do not know data
locations in advance. The destination of data is, hence, unknown when data are
generated. This communication paradigm differs from publish/subscribe systems in
which data are forwarded by broker nodes to users according to their data
subscriptions. Appropriate network design is needed to ensure that data can be
promptly accessed by requesters in such cases.
PROBLEM STATEMENT
A common technique used to improve data access performance is caching, i.e., to
cache data at appropriate network locations based on query history, so that queries
in the future can be responded with less delay. Although cooperative caching has
been studied for both web-based applications and wireless ad hoc networks to
allow sharing and coordination among multiple caching nodes, it is difficult to be
realized in DTNs due to the lack of persistent network connectivity. First, the
opportunistic network connectivity complicates the estimation of data transmission
delay, and furthermore makes it difficult to determine appropriate caching
locations for reducing data access delay. This difficulty is also raised by the
incomplete information at individual nodes about query history. Second, due to the
uncertainty of data transmission, multiple data copies need to be cached at different

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locations to ensure data accessibility. The difficulty in coordinating multiple
caching nodes makes it hard to optimize the tradeoff between data accessibility and
caching overhead.
PROBLEM SOLUTION
A novel scheme to be proposed address the aforementioned challenges and to
efficiently support cooperative caching in DTNs. Intentionally cache data at a set
of network central locations (NCLs), each of which corresponds to a group of
mobile nodes being easily accessed by other nodes in the network. Each NCL is
represented by a central node, which has high popularity in the network and is
prioritized for caching data. Due to the limited caching buffer of central nodes,
multiple nodes near a central node may be involved for caching, and it ensures that
popular data are always cached nearer to the central nodes via dynamic cache
replacement based on query history. To develop an efficient approach to NCL
selection in DTNs based on a probabilistic selection metric. The selected NCLs
achieve high chances for prompt response to user queries with low overhead in
network storage and transmission. To propose a data access scheme to
probabilistically coordinate multiple caching nodes for responding to user queries.

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EXISTING SYSTEM
 Data forwarding in DTNs originates from Epidemic routing, which floods
the entire network.
 Efficient relay selection metrics were proposed to approach the performance
of Epidemic routing with lower forwarding cost, based on prediction of node
contacts in the future.
 The social network properties of node contact patterns, such as the centrality
and community structures, have also been also exploited for relay selection
in recent social-based data forwarding schemes.
 Compare-and-Forward method is used, where a relay forwards data to
another node whose metric value is higher than itself.
 Delegation forwarding reduces forwarding cost by only forwarding data to
nodes with the highest metric.
 Data access in DTNs, provided in various ways, data can be disseminated to
appropriate users based on their interest profiles. Publish/ subscribe systems
were used for data dissemination, where social community structures are
usually exploited to determine broker nodes.
 Caching is another way to provide data access. Cooperative caching in
wireless ad hoc networks was studied, in which each node caches pass-by

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data based on data popularity, so that queries in the future can be responded
with less delay.
Disadvantages
 Always keeps a single data copy and Spray-and-Wait holds a fixed number
of data copies, most schemes dynamically determine the number of data
copies.
 Under cooperative caching, Peer-to-peer data sharing and access among
mobile users are generally neglected.
PROPOSED SYSTEM
 To propose a novel scheme to address the aforementioned challenges and to
efficiently support cooperative caching in DTNs.
 Intentionally cache data at a set of network central locations (NCLs), each of
which corresponds to a group of mobile nodes being easily accessed by
other nodes in the network.
 Each NCL is represented by a central node, which has high popularity in the
network and is prioritized for caching data.
 Due to the limited caching buffer of central nodes, multiple nodes near a
central node may be involved for caching, and it ensures that popular data

LeMeniz Infotech
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are always cached nearer to the central nodes via dynamic cache
replacement based on query history.
 To develop an efficient approach to NCL selection in DTNs based on a
probabilistic selection metric. The selected NCLs achieve high chances for
prompt response to user queries with low overhead in network storage and
transmission.
 To propose a data access scheme to probabilistically coordinate multiple
caching nodes for responding to user queries.
 To propose a utility-based cache replacement scheme to dynamically adjust
cache locations based on query history
Advantages
 Optimize the tradeoff between data accessibility and caching overhead, to
minimize the average number of cached data copies in the network.
 Achieves good tradeoff between the data accessibility and access delay.
LITERATURE SUMMARY
Research on data forwarding in DTNs originates from Epidemic routing, which
floods the entire network. Some later studies focus on proposing efficient relay
selection metrics to approach the performance of Epidemic routing with lower
forwarding cost, based on prediction of node contacts in the future. Some schemes

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do such prediction based on their mobility patterns, which are characterized by
Kalman filter or semi-Markov chains.
In some other schemes, node contact pattern is exploited as abstraction of node
mobility pattern for better prediction accuracy, based on the experimental and
theoretical analysis of the node contact characteristics. The social network
properties of node contact patterns, such as the centrality and community
structures, have also been also exploited for relay selection in recent social-based
data forwarding schemes. The aforementioned metrics for relay selection can be
applied to various forwarding strategies, which differ in the number of data copies
created in the network. While the most conservative strategy always keeps a single
data copy and Spray-and-Wait holds a fixed number of data copies, most schemes
dynamically determine the number of data copies.
In Compare-and-Forward, a relay forwards data to another node whose metric
value is higher than itself. Delegation forwarding reduces forwarding cost by only
forwarding data to nodes with the highest metric. Data access in DTNs, on the
other hand, can be provided in various ways. Data can be disseminated to
appropriate users based on their interest profiles.
Publish/ subscribe systems were used for data dissemination, where social
community structures are usually exploited to determine broker nodes. In other
schemes without brokers, data items are grouped into predefined channels, and are
disseminated based on users’ subscriptions to these channels. Caching is another

LeMeniz Infotech
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95663 55386.
/9566355386
way to provide data access. Cooperative caching in wireless ad hoc networks was
studied, in which each node caches pass-by data based on data popularity, so that
queries in the future can be responded with less delay. Caching locations are
selected incidentally among all the network nodes.
Some research efforts have been made for caching in DTNs, but they only improve
data accessibility from infrastructure network such as WiFi access points (APs) or
Internet. Peer-to-peer data sharing and access among mobile users are generally
neglected. Distributed determination of caching policies for minimizing data
access delay has been studied in DTNs, assuming simplified network conditions.
It is assumed that all the nodes contact each other with the same rate. Users are
artificially partitioned into several classes such that users in the same class are
identical. Data are intentionally cached at appropriate network locations with
generic data and query models, but these caching locations are determined based
on global network knowledge.

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HARDWARE REQUIREMENTS
Processor : Any Processor above 500 MHz.
Ram : 128Mb.
Hard Disk : 10 Gb.
Compact Disk : 650 Mb.
Input device : Standard Keyboard and Mouse.
Output device : VGA and High Resolution Monitor.
SOFTWARE SPECIFICATION
Operating System : Windows Family.
Pages developed using : Java Swing
Techniques : JDK 1.5 or higher
Database : MySQL 5.0

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Query Reply
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SYSTEM ARCHITECTURE
Node A Query
Nearest
NCL
Server
Allocate
NCL
Query Reply
Cache
memory
Node Query
NCL – Network Central Location

Cooperative caching for efficient data access in disruption tolerant networks

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